Low cost dispersive optical elements

ABSTRACT

A dispersive optical element includes a substrate including a dielectric material, an optical coating arranged on the substrate, and a layer of material including a microscale feature arranged directly on the optical coating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 15/889,452,filed Feb. 6, 2018, the contents of which are hereby incorporated byreference in its entirety.

BACKGROUND

The present disclosure relates to optical elements, and morespecifically, to dispersive optical elements.

Diffraction gratings are used in various devices, for example,monochromators and spectrometers. In optics, a diffraction grating is anoptical component with a periodic structure that splits and diffractslight into several beams travelling in different directions. Thedirections of the emerging beams depend on the spacing of the elementsof the period structure and the wavelength of the light. Diffractiongratings generally have ridges or rulings on their surface with spatialfrequencies of about a wavelength. Such gratings can be eithertransmissive or reflective.

Traditional manufacturing techniques for forming materials andstructures for diffraction gratings include semiconductor subtractivemanufacturing processes. Such processes include building up material andthen removing the material by masking (lithography) and etchingprocesses. For example, subtractive manufacturing methods can includecoating with a photoresist, exposing the photoresist to radiation,etching with reactive materials, and then removing the residualmaterial.

SUMMARY

According to one or more embodiments, a dispersive optical elementincludes a substrate including a dielectric material, an optical coatingarranged on the substrate, and a layer of material including amicroscale feature arranged directly on the optical coating.

According to one or more embodiments, a dispersive optical elementincludes a substrate including a dielectric material, a first opticalcoating arranged on the substrate, and a layer of material including amicroscale feature arranged directly on the first optical coating. Asecond optical coating is on the substrate on a side opposing the firstoptical coating.

According to one or more embodiments, a method of making a dispersiveoptical element including forming a film including microscale featuresby a roll printing process and attaching the film to a substrateincluding an optical coating. The film is attached directly to theoptical coating.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts:

FIG. 1 is a side view of a dispersive optical element with a layer ofmaterial with microscale features arranged on a coated substrate;

FIG. 2 is a side view of dispersive optical dispersive element with alayer of material with microscale features arranged on a substratecoated on both sides;

FIG. 3 is a side view of a dispersive optical element with a layer ofmaterial with microscale features arranged on a substrate;

FIG. 4 is a side view of a dispersive optical element with a layer ofmaterial with microscale features arranged on a substrate with anantireflective coating;

FIG. 5 is a side view of a dispersive optical element with a layer ofmaterial with microscale features arranged on a substrate with a highreflecting coating in between the layer of material and the substrate;and

FIG. 6 is a dispersive optical element with a layer of material withmicroscale features arranged on a substrate with an absorbing materialin between the layer of material and the substrate.

DETAILED DESCRIPTION

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, traditional subtractivemanufacturing techniques for making dispersive optical elements(diffraction gratings), particularly etching, can lead to defects in theetched material and the substrate beneath. Subtractive manufacturingtechniques also use cleaning processes that can contaminate the etchedsurface and lead to significant reduction in the damage threshold. Thecosts of these processes are also high due to the number of processingsteps involved.

Given the challenges of traditional lithography and etching processesfor forming diffraction gratings, various attempts have been made toimprove these processes. For example, the traditional subtractivemanufacturing processes have been automated. Modifications to theprocessing steps have also been made in attempts to minimize defects andcontamination. However, even such variations to the traditionalsubtractive methods are high cost and lead to defects in the gratingsand substrates.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings byproviding a lower cost method of making a dispersive optical elementthat utilizes additive manufacturing methods instead of conventionalsubtractive methods. Materials with microscale features are formed byroll printing manufacturing methods, and the material is then adhered toeither an uncoated or coated substrate. Using the roll printed materialsenables a variety of materials to be used for the dispersive elements,including for example, sintered ceramic materials, gold coated ceramicpowders, doped ceramic powders, ultraviolet (UV) cured ceramic powders,and self-assembling polymers. The depth, width and spacing of themicroscale features can also be varied across the width of the rollerand over a distance up to the circumference of the roller. The depth,width and spacing of the microscale feature can also be varied along thecircumference of the roller up to the width of the roller. An additionaladvantage of additive manufacturing methods is that they are lowtemperature processes that enable dispersive materials to be created onsubstrates coated with optical materials, such as antireflectivecoatings and high reflecting coatings that could not withstand hightemperatures or residual stress of conventional subtractivemanufacturing methods.

The dispersive optical elements disclosed herein can be used in avariety of applications, including but not limited to, monochromators,spectrometers, lasers, wavelength division multiplexing devices, opticalpulse compressing devices, and other optical instruments.

As used herein, the terms “light” or “electromagnetic radiation” referto light having a wavelength in the ultraviolet region, visible region,infrared region, microwave region, and/or radio wave region of theelectromagnetic spectrum.

The dispersive optical elements described herein diffract light ofwavelengths in the ultraviolet region of the electromagnetic spectrum(0.01 to 0.4 micrometers or microns), visible region (0.4 to 0.7micrometers), infrared region of the electromagnetic spectrum (0.7 to1,000 micrometers), microwave region of the electromagnetic spectrum(1,000 to 1,000,000 micrometers), and/or radio wave region of theelectromagnetic spectrum (1,000,000 to 10,000,000,000,000 micrometers).

Turning now to a more detailed description of aspects of the presentinvention, FIG. 1 is a side view of a dispersive optical element havinga material with microscale features arranged on a coated substrateaccording to embodiments of the invention. The substrate 101 is a rigidsurface that provides mechanical support to the dispersive opticalelement. The substrate 101 includes one or more materials, such as oneor more dielectric materials. Non-limiting examples of dielectricmaterials include magnesium fluoride, silicon dioxide, aluminum oxide,aluminum fluoride, cerium fluoride, lanthanum fluoride, neodymiumfluoride, samarium fluoride, barium fluoride, calcium fluoride, lithiumfluoride, and the like. Other suitable dielectric materials include zincsulfide, zinc oxide, zirconium oxide, titanium dioxide, diamond-likecarbon, indium oxide, indium-tin-oxide, tantalum pentoxide, ceric oxide,yttrium oxide, europium oxide, iron oxides such as (II) di-iron(III)oxide and ferric oxide, hafnium nitride, hafnium carbide, hafnium oxide,lanthanum oxide, magnesium oxide, neodymium oxide, praseodymium oxide,samarium oxide, antimony trioxide, silicon, silicon monoxide, silicondioxide, glass, selenium trioxide, tin oxide, tungsten trioxide, and thelike. Various mixtures or combinations of the above dielectric materialscan also be employed. The thickness of the substrate 101 can vary anddepends on the particular application for the dispersive opticalelement. According to one or more embodiments, the thickness of thesubstrate 101 is about 100 to about 100,000 micrometers. According toother embodiments, the thickness of the substrate 101 is about 1,000 toabout 10,000 micrometers. The substrate 101 can transmit or absorb lightof a given wavelength, depending on the particular application.

The material(s) forming the substrate 101 are selected and tailored suchthat they exhibit the desired optical response when irradiated with abeam of electromagnetic radiation in the ultraviolet wavelength range(0.01 to 0.4 micrometers), visible wavelength range (0.4 to 0.7micrometers), infrared wavelength range (0.7 to 1,000 micrometers),microwave wavelength range (1,000 to 1,000,000 micrometers), or radiowavelength range (1,000,000 to 10,000,000,000,000 micrometers).Depending on the selection of materials, the substrate 101 transmits orabsorbs light of a given wavelength in the ultraviolet, visible,infrared, microwave, or radio wavelength range.

An optical coating 102 is arranged on the substrate 101. The opticalcoating 102 is one or more thin layers of material deposited onto thesubstrate 101 that alters the way in which the substrate in combinationwith the coating reflects and transmits light. According to one or moreembodiments, the light is ultraviolet, visible, infrared, microwave orradio wavelength light. The optical coating 102 is applied to onesurface (one side) of the substrate 101 directly beneath the material103 with microscale features, as shown in FIG. 1 , in some embodiments.The optical coating 102 is also applied to two surfaces, first andsecond surfaces (opposing sides) of the substrate 101, as opticalcoating 102 and 202, as shown in FIG. 2 in other embodiments. Accordingto one or more embodiments, the dispersive optical element includes alayer of material 103 including a microscale feature arranged directlyon the substrate 101 (without a coating arranged therebetween), as shownin FIG. 3 .

The optical coating 102 includes one layer (monolayer) or more than onelayer (multilayers). When the optical coating 102 includes more than onelayer, the materials forming the different layers can include differentmaterials.

The optical coating 102 can be a thin layer(s) of metal, for example,aluminum, silver, or gold. The optical coating 102 can be a dielectriccoating of a material with a different refractive index than thesubstrate 101. The dielectric coating includes thin layers of materials,for example magnesium fluoride, calcium fluoride, and various metaloxides.

The optical coating 102 can be a thin film of material, such as anantireflective (AR) coating or a high reflecting (HR) coating.Antireflective coatings are coatings that at least partially improve theantireflective nature of the substrate to which it is applied byreducing the amount of glare reflected by the surface of the substrate.For transparent substrates, antireflective coatings increase the percenttransmittance as compared to an uncoated substrate. Non-limitingexamples of antireflective coatings include a monolayer or multilayer ofmetal oxide (such as silicon dioxide), a metal fluoride, a metalnitride, a metal sulfide, or the like. An antireflective coating can bedeposited onto the substrate 101 through, for example, vacuumevaporation, sputtering, or other suitable methods.

High reflecting coatings increase the overall reflectivity of thesubstrate surface and include one or more layers of dielectric materialsand/or metals. Non-limiting examples of metals include aluminum, gold,silver, copper, nickel, platinum, and rhodium.

Thin film optical coatings, such as AR and HR coatings, can be easilydamaged and therefore cannot be formed beneath a diffraction gratingformed from conventional lithography and etching processing methods.However, as described herein, using a material 103 with already formedmicroscale features enables direct application to the rigid substrate101 that can be coated with any desired optical coating 102. Theintegrity of the optical coating 102 is maintained due to lowtemperature processing used to adhere the material 103 to the coatedsubstrate.

The material 103 is a film that includes microscale features formed byroll printing methods, such as roll-to-roll printing processes, in someembodiments. Roll printing processes use direct mechanical deformationto imprint microscale features (or patterns) into a thin layer ofmaterial. Such features are formed by methods that include one or morerotatable rollers, with at least one of the rollers having a pluralityof protrusions that defines the pattern (with microscale features) to beapplied to the material. The thin layer of material to be patterned isarranged between the patterning roller, a backing material, and a secondroller or a substrate. As the rotatable rollers rotate, the thin layerof material is patterned with microscale features and adhered to thebacking material.

The microscale features formed on the material 103 can be periodic andregular, or irregular. The microscale features on the surface of thematerial 103 are a plurality of grooves 130 having a depth (d) and width(w) with spacings (s) therebetween (see FIG. 1 ). Any or all of thesedimensions are microscale. The microscale features have at least onedimension (depth, width, or spacing) that is less than about 100micrometers is some aspects, less than 10 micrometers in other aspects,and less than 1 micrometer in some aspects. According to one or moreembodiments, the microscale features have at least one dimension (depth,width, or spacing) that is about 0.1 micrometer. The microscale featureshave at least one dimension that is less than about 0.5 micrometers insome aspects, less than 0.1 micrometer in other aspects, and less than0.01 micrometers in some aspects. As used herein, reference tomicroscale encompasses smaller structures, such as the equivalentnanoscale features. In some aspects, the microscale features have atleast one dimension that is in a range from about 0.01 micrometers to1000 micrometers.

According to one or more aspects, the material 103 includes a pluralityof grooves with dimensions of 1×1×1 micrometer in depth, width andspacing. According to exemplary aspect, the material 103 includes aplurality of grooves with dimensions of 0.5×0.5×0.5 micrometers indepth, width, and spacing. According to some aspects, the material 103includes a plurality of grooves with dimensions of 10×10×10 micrometersin depth, width, and spacing. According to other aspects, the material103 includes at least one microscale feature having dimensions (gratingspacings) in the ultraviolet, visible, infrared, microwave, or radiowavelength range.

Using roll printing processes to form the material 103 with themicroscale features is advantageous because such methods arecost-effective. Rolls and machinery for forming the sheets of materialare scaled up so that large sheets can be formed rapidly. Large sheetsof material can then be cut to any desired size, for example into sheetshaving widths from 1 to 8 inches before adhering to the coatedsubstrate.

Roll printing is used to rapidly and easily form the material 103 withthe microscale features of any size that is then applied to thesubstrate 101 with the optical coating 102. The material 103 is adheredor attached by any suitable methods. The material 103 directly adheresto the optical coating 102 in some aspects (as shown in FIGS. 1 and 2 ).The material 103 also can adhere directly to the substrate 101 in otheraspects (as shown in FIG. 3 ). In these embodiments, no additionalmaterial is need to directly stick the material 103 to the rigidsubstrate. In other embodiments, the material 103 is attached to thesubstrate 101 and/or coating with an adhesive arranged therebetween. Thesubstrate 101 with the coating 102 provides a rigid surface for thematerial 103. Without the rigid surface of the substrate 101, the thinfilm of material 103 may not be stable as it could be easily damagedwhen stretched or applied to a surface without the substrate 101.

The materials and ordered pattern of the material 103 are selected toproduce an optical response in the ultraviolet, visible, infrared,microwave, or radio wavelength region of the electromagnetic spectrum.The roller dimensions and patterns used to form the microscale featuresin the material 103 are varied to create the desired pattern.

The material 103 with microscale features may be formed of any suitablematerial, such as a ceramic material in some embodiments. The ceramicmaterial may be a sintered ceramic material coated with a metal. A metalor a material including a metal is applied on the surface of the curedceramic material. The metal material can be applied by a variety ofsuitable processes, including at least one process selected from:chemical vapor deposition, physical vapor deposition, shadowevaporation, and sputter deposition. While the desired metal dependsupon the end-use application, the metal material can include, but is notlimited to, gold, platinum, silver, copper, aluminum, chromium, nickel,titanium and mixtures and alloys thereof.

The ceramic material may be a sintered metal oxide. Non-limitingexamples of metal oxides include aluminum oxide, titanium dioxide, orindium tin oxide. The ceramic material may be doped with rare earthmaterials. A material that is formed of a doped metal oxide may not havea coating of additional electrically conductive material, but anoptional step includes coating a top surface of a sintered ceramicmaterial with any suitable electrically conductive material. An exampleof a suitable coating material may be silver and the coating may have athickness of less than 1 micron.

In another configuration of materials, the material 103 with microscalefeatures may be formed of one or more curable polymer precursor, such asmonomers or oligomers. Curable polymers are capable of undergoing apolymerization reaction when exposed to certain forms of energy, such asheat and/or actinic radiation (such as UV irradiation). Curing reactionscan be initiated by activation of a curing agent species and can proceedby a cationic route or a free radical route, for example. In suchembodiments, a liquid conductive polymeric precursor material isroll-printed to a sheet of polymeric material. The liquid is cured to asolid after printing. Non-limiting examples of curable polymerprecursors include an epoxy precursor, epoxysiloxane precursor, negativetone photoresist precursor that undergoes UV radiation curing.Optionally, a metal or a material including a metal is applied on thesurface of the cured polymeric material. The metal material can beapplied by a variety of suitable processes, including at least oneprocess selected from: chemical vapor deposition, physical vapordeposition, shadow evaporation, and sputter deposition. While thedesired metal depends upon the end-use application, the metal materialcan include, but is not limited to, gold, platinum, silver, copper,aluminum, chromium, nickel, titanium and mixtures and alloys thereof.

In still another configuration of materials, two block copolymers may beused for roll-printing the material 103 with microscale features. Theblocks of copolymers may self-assemble into the plurality of groovesforming the microscale features on the surface of the material 103.

The material used to form the material 103 with microscale features maybe selected to produce an optical response in a particular portion ofthe electromagnetic spectrum. The material 103 may be tailored toreflect or transmit light in the ultraviolet, visible, infrared,microwave region, and/or radio wave region of the electromagneticspectrum, for example.

FIGS. 4-6 illustrate how the properties of the optical coating 102 andsubstrate 101 can be tailored to alter the reflectance or transmittanceproperties of the dispersive optical element.

FIG. 4 is a side view of a dispersive optical element in which theoptical coating 102 is an antireflective coating. In the embodimentsshown in FIG. 4 , the dispersive optical element includes a layer ofmaterial with microscale features arranged on a substrate with anantireflective coating as the optical coating 102. The dispersiveoptical element is irradiated with a beam of electromagnetic radiation(for example a beam with a range of wavelengths in the ultraviolet,visible, infrared, microwave, or radio wavelength range). The material103 with microscale features interacts with a portion of the light (oneor more wavelengths of light) and is transparent to another portion ofthe light (one or more wavelengths of light). According to one or moreembodiments, the one or more wavelengths of light is in the ultraviolet,visible, infrared, microwave, or radio wavelength range. According toembodiments, the layer of material 103 with the microscale featurediffracts light of a first wavelength (or wavelengths) and istransparent to light of a second wavelength (or wavelengths), and theoptical coating 102 transmits light of the second wavelength (orwavelengths). The material 103 disposed on the antireflective coatingallows for absorption or separation of unwanted light. In an exemplaryembodiment, the electromagnetic beam includes light having λ₁ 411 and λ₂410. The material 103 with microscale features interacts with anddiffracts light of λ₁ 411 and is transparent to (transmits) light of λ₂410. The antireflective coating (optical coating 102) and the substrate101 transmit light of λ₂ 410 (are transparent to light of λ₂ 410).

The dispersive optical element shown in FIG. 4 optionally includes asecond coating 202 arranged on the other side of the substrate 101. Theoptical coating 202 is configured to enhance the performance of theoptical dispersive element by either enhancing the transmission of light410 through the substrate 101 and through the coating 202 or enhancingthe transmission of light through the substrate and reducing thetransmission through the coating 202 to guide the light within thesubstrate. For enhancing transmission, the second coating 202 includes,for example, thin layers of dielectric materials, for example magnesiumfluoride, calcium fluoride, and various metal oxides. For reducing thetransmission through coating 202, thin metals, for example, aluminum,silver, or gold may be used.

FIG. 5 is a side view of a dispersive optical element in which theoptical coating 102 is a high reflecting coating. In the embodimentsshown in FIG. 5 , the dispersive optical element includes a layer ofmaterial 103 with microscale features arranged on a substrate 101 with ahigh reflecting coating in between the layer of material and thesubstrate. The optical dispersive element is irradiated with a beam ofelectromagnetic radiation (for example a beam with a range ofwavelengths in the ultraviolet, visible, infrared, microwave, or radiowavelength range). The material 103 with microscale features interactswith a portion of the light (one or more wavelengths of light) and istransparent to another portion of the light (one or more wavelengths oflight). According to embodiments, the layer of material 103 comprisingthe microscale feature diffracts light of a first wavelength (orwavelengths) and is transparent to light of a second wavelength (orwavelengths), and the optical coating 102 reflects light of the secondwavelength (or wavelengths). The material 103 disposed on the highreflecting coating (optical coating 102) allows the dispersive opticalelement to reflect the light that the material 103 transmits. In anexemplary embodiment, the electromagnetic beam includes light having λ₁511 and λ₂ 510. The material 103 with microscale features interacts withand diffract light of λ₁ 511 and is transparent to (transmits) light ofλ₂ 510. The high reflecting coating (optical coating 102) reflects lightof λ₂ 510.

FIG. 6 is a dispersive optical element in which the optical coating 102an absorbing material. In the embodiments shown in FIG. 6 , thedispersive optical element includes a layer of material 103 withmicroscale features arranged on a substrate 101 with an absorbingmaterial in between the layer of material 103 and the substrate 101. Theoptical dispersive element is irradiated with a beam of electromagneticradiation (for example a beam with a range of wavelengths in theultraviolet, visible, infrared, microwave, or radio wave range). Thematerial 103 with microscale features interacts with a portion of thelight (one or more wavelengths of light) and is transparent to anotherportion of the light (one or more wavelengths of light). In an exemplaryembodiment, the electromagnetic beam includes light having λ₁ 611 and λ₂610. The material 103 with microscale features interacts with anddiffract light of λ₁ 611 and is transparent to (transmits) light of λ₂610. The absorbing material (optical coating 102) absorbs light of λ₂610. Non-limiting examples of absorbing materials include silicon (forabsorbing wavelengths less than about 1 micron), germanium (forabsorbing wavelengths about or less than 2 microns), and magnesiumfluoride (for absorbing wavelengths greater than about 9 microns). Insome embodiments, the absorbing material is a semiconductor material.

The dispersive optical element shown in FIG. 6 optionally includes asecond optical coating 202 arranged on the other side of the substrate101. The coating 202 is configured to enhance the performance of theoptical dispersive element by either enhancing the transmission of light610 through the substrate 101 and through the coating 202 or enhancingthe transmission of light through the substrate and reducing thetransmission through the coating 202 to guide the light within thesubstrate.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Accordingly, a coupling of entities can refer to either adirect or an indirect coupling, and a positional relationship betweenentities can be a direct or indirect positional relationship. As anexample of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

The phrase “selective to,” such as, for example, “a first elementselective to a second element,” means that the first element can beetched and the second element can act as an etch stop.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

It will also be understood that when an element, such as a layer,region, or substrate is referred to as being “on” or “over” anotherelement, it can be directly on the other element or intervening elementsmay also be present. In contrast, when an element is referred to asbeing “directly on” or “directly over” another element, there are nointervening elements present.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

What is claimed is:
 1. A method of making a dispersive optical element,the method comprising: forming a film comprising microscale features;and attaching the film to an optical coating that is on a substrate, thefilm attached directly to the optical coating; wherein the film is asintered metal oxide, a sintered ceramic material, a curable polymer, ora self-assembled block copolymer.
 2. The method of claim 1, wherein thesubstrate comprises a dielectric material.
 3. The method of claim 1,wherein the optical coating is an antireflective coating or a highreflecting coating.
 4. The method of claim 1, wherein the filmcomprising microscale features diffracts light of a first wavelength andis transparent to light of a second wavelength, and the optical coatingreflects or transmits light of the second wavelength.
 5. The method ofclaim 1, wherein the film further comprises a metal layer.